The objective of the present research is to improve the calibration of electrophoretic short tandem repeat (STR) analysis so as to facilitate its widespread use in human identification with simple, cost effective, reproducibly and highly discriminating electrophoretic systems. The primary sequence of a DNA fragment affects its electrophoretic mobility, rendering it imprecise in calibration of DNA from a different genetic locus. Complicated mechanisms have been applied to correct this error. They require multiple laser excited fluorophores, elaborate systems to differentiate their emission spectra, coelectrophoresis in external lanes of allelic ladders from loci to be typed, and increased computation time and labor. Locus specific brackets (LSB) are created through modification of alleles from each genetic locus to be measured. Closely related in both sequence and lengths to the alleles of their loci of origin, they provide compatible electrophoretic mobility for calibration of fragment length measurement Multiplexes of LSB will he developed for the 13 STR loci employed in the national forensic database (CODIS) under development by the FBI. Accurate, less expensive, and user friendly calibration will increase it application to other areas of interest such as paternity, antenatal diagnosis, gene mapping, loss of heterozygosity, and tissue typing. PROPOSED COMMERCIAL APPLICATIONS: Human identification in criminal justice. Paternity. Antenatal testing for chromosomal defects. Tissue typing in transplantation. Gene mapping. Carcinogenesis through loss of heterozygosity.